When a cross hole is formed on a workpiece of a hollow rod material whose sections of both the outer peripheral surface and the inner peripheral surface are circular by using a conical tool having a conical cutting blade, the opening edge part of the cross hole is formed into an inclined surface along the arc of the outer and inner peripheral surfaces.
FIGS. 13A and 13B are diagrams explaining the case where the chamfer machining is carried out on an opening edge part of a cross hole from the outer diameter side of a workpiece of hollow rod material by using a conical tool, and FIG. 13A is a perspective view and FIG. 13B is a top view.
If the chamfer machining is carried out on the opening edge part from the outside of a workpiece W by using a conical tool, the amount of chamfering is not uniform, since the opening edge part of a cross hole 2-1 that is formed gradually changes from an inclined surface into a substantially flat surface along the curvature of the outer peripheral surface of the workpiece W, and then, further changes into an inclined surface, and the degree in which the cutting blade of the conical tool comes into contact with the opening edge part is different, and therefore there will be a part that is more chamfered and a part that is less chamfered. In other words, in the arc center axis line direction of the workpiece W, the conical tool comes into contact strongly and deeply, but in the direction perpendicular to the arc center axis line of the workpiece W, the conical tool comes into contact weakly and shallowly, and as a result, chamfering will result in an ellipse elongated in the arc axis line direction.
FIGS. 14A and 14B are diagrams explaining the case where the chamfer machining is carried out on an opening edge part of a cross hole from the inner diameter side of a workpiece of hollow rod material by using a conical tool, and FIG. 14A is a perspective view and FIG. 14B is a top view.
If chamfer and drilling machining is carried out on the opening edge part from the inside of the hollow portion of the workpiece W by using a conical tool, the amount of chamfering is not uniform, since the opening edge part of a cross hole 2-2 that is formed gradually changes from an inclined surface into a substantially flat surface along the curvature of the inner peripheral surface of the workpiece W, and then, further changes into an inclined surface, and the degree in which the cutting blade of the conical tool comes into contact with the opening edge part is different, and therefore there will be a part that is more chamfered and a part that is less chamfered. In other words, in the direction perpendicular to the arc center axis line direction of the workpiece W, on the contrary to the case of the outer peripheral surface explained in FIGS. 13A and 13B, the conical tool comes into contact strongly and deeply, but in the arc center axis line direction of the workpiece W, the conical tool comes into contact weakly and shallowly, and as a result, chamfering will result in an ellipse elongated in the direction perpendicular to the arc axis line.
Further, also in the case where the opening edge part of the cross hole that is formed on the workpiece is an opening edge part formed inclined with respect to the surface of the workpiece, the shape on the surface of the opening edge part is the shape of an ellipse, and therefore the opening edge part of the cross hole that is formed is not the shape of a cylinder whose axis center is the rotation axis of the conical tool.
Several chamfering devices and methods for carrying out chamfer machining on the opening edge portion of a cross hole having such an inclination have been proposed.
For example, there is a chamfering device whose chamfering bar for removing burrs generated around the hole entrance is made compact so as to be capable of being inserted into a narrow space (e.g., see Patent Document 1).
Further, for example, there is a method for removing burrs generated on the peripheral edge part on the backside of a through hole having a circular section, which is formed on the workpiece, from the surface side of the workpiece (e.g., see Patent Document 2).
Furthermore, for example, there is a grinding tool that has a grindstone and a holder that holds the grindstone, which is capable of appropriately grinding an area to be machined on the backside of a workpiece without the need to make troublesome adjustment by causing the grindstone to come into contact with the backside of the workpiece at all times even if the grindstone wears or there are bumps and dips in the area to be machined of the workpiece by causing the grinding tool to have such a structure in which a first biasing member that biases the grindstone toward the holder side as well as supporting the grindstone so as to be movable in both directions in the axis line direction of the holder is provided in the holder, and in which the grindstone comes into contact with the workpiece with an optimum load in accordance with the biasing force of the first biasing member without the need to carry out control of the position in the axis line direction of the grindstone with respect to the workpiece with a high accuracy (e.g., see Patent Document 3).
For example, there is a corner part machining tool having a main body in which a space through which cutting fluid can pass is formed and a blade part provided in the main body and capable of changing its position to the outside of the main body, and machining a corner part by the blade part by changing the position of the blade part to the outside of the main body in accordance with a change in the static pressure of the cutting fluid having passed through the space and by rotating the main body (e.g., see Patent Document 4).